This is a very common question that most people don't know the answer to. It all started in 1964. To compete with Pontiac's GTO, Oldsmobile launched their own high performance option on the intermediate-size F85's and Cutlasses. It stood for four-barrel carburetor, four-speed transmission, and dual exhaust.
In 1965, Oldsmobile introduced their new 400 cubic inch engine. Also, they wanted to give prospective 442 buyers a choice of automatic or standard transmission. So, 442 stood for 400 cu in engine, 4 bbl carburetor, and dual exhaust now.
In 1968, the 442 graduated to it's own model status. It also marked the beginning of the W options, namely the W30. The 400 engine remained until 1970.
In 1970, the muscle car era peeked and with it came the new 455 cu in engine. W30, W31, and W32, and the W45 Rallye 350 were all redone W options. So the first 4 in 442 stood for 455 cu in now. The 4 bbl carburetor and dual exhaust remained.
In 1972, the 442 lost it's model status. The 442 option code was W29. If you wanted a 442 now, you ordered your base model Cutlass and then ordered the W29 option. The 350 engine was now standard, although you could still order the 455, but it was down on compression from 10.5:1 to 8.5:1 due to the new emissions requirements.
The 442 option continued this way well into the 1970's and early 1980's as the W29 option. In 1985, it stood for 4 speed automatic, 4 bbl, dual exhaust.
In 1990, it stood for 4 cylinders, 4 valves and 2 camshafts.
Here are some links with more info on 442's and W codes: